内容来源：https://www.quantamagazine.org/are-memories-transferable-or-edible-20260605/

内容总结：

震惊！60年前轰动科学界的“记忆可食用”实验，如今竟无法复现

波士顿讯 在科学史上，曾有一项令人匪夷所思的实验：将一只经过训练的蠕虫剁碎，喂给另一只蠕虫，后者竟然“继承”了前者的记忆。这项由20世纪60年代心理学家詹姆斯·麦康奈尔主导的研究，一度被认为是颠覆认知的重大发现。然而，60年后的今天，当哈佛大学的科学家试图复现这一经典实验时，却遭遇了令人困惑的失败——那些蠕虫，竟然再也不肯学习了。

备受争议的“食人记忆”实验

故事要从上世纪50年代说起。当时还是研究生的麦康奈尔提出了一个大胆问题：记忆是否具有化学基础？他选择了一种名叫“涡虫”的扁平蠕虫作为实验对象。这种生物虽然简单，却拥有真正的神经系统和惊人的再生能力——即使被切成两半，每一半都能重新长成完整的个体。

麦康奈尔的实验方法堪称粗暴：他先将涡虫置于强光下并施以电击，反复训练后，涡虫学会了一见光就缩身。接着，他将这些“受过教育”的涡虫剁成肉泥，喂给其他未受训练的同类。令人震惊的是，这些“食人”的涡虫似乎真的“继承”了前者的记忆，无需训练就对光线产生反应。

更离奇的是，麦康奈尔还发现，即便把训练过的涡虫砍掉脑袋，从尾巴再生出来的新头部仍然保留着那段记忆。这意味着，记忆似乎不局限于大脑，而是散布在整个身体中。麦康奈尔由此认为，记忆可能被编码在RNA分子中，通过“进食”实现转移。

“蠕虫训练”风靡一时

凭借出色的媒体嗅觉，麦康奈尔将自己打造成了一位科学明星。他接受《时代》杂志专访，登上史蒂夫·艾伦秀电视节目，甚至自封“麦食人魔”，畅想未来人类可以服用“钢琴课药丸”或食用“教授汉堡”来获取知识。

他创办的《蠕虫跑者文摘》更像是一本科学版的《疯狂杂志》，既有严肃论文，也有科幻小说和学生漫画，订阅高峰时达到2500份。在麦康奈尔的推动下，“蠕虫训练”一度成为美国高中科学展的热门项目，至少36家实验室报告了类似的成功结果。

辉煌落幕，科学悬案留存

然而，好景不长。上世纪60年代中期，诺贝尔奖得主梅尔文·卡尔文尝试复现麦康奈尔的实验，却宣告失败。关于“记忆转移”的争议愈演愈烈，许多实验室无法稳定复现其结果。到70年代，这场科学热潮逐渐消退。麦康奈尔于1971年关闭实验室，1990年去世。他的“食人涡虫”实验，终究成了一个科学史上的谜案。

“这段经历如今被神经科学家当作睡前恐怖故事，用来警告学生远离注定失败的项目。” 哈佛大学神经科学家萨姆·格什曼这样形容。

60年后：蠕虫们学会了“罢工”

格什曼正是那位试图解开这个半个世纪悬案的科学家。2025年，他和博士后研究员玛蒂·斯奈德决定严格按照麦康奈尔学生艾伦·雅各布森的实验方案，复现当年的“涡虫学习”实验。

然而，无论他们如何尝试——更换刺激方式、调整实验参数、甚至拜访博物馆研究当年的电击装置——结果都是失败。那些涡虫，就是学不会。

“我简直抓破脑袋。”格什曼说。他原以为“记忆转移”部分才可能出问题，没想到连最基础的“让涡虫学习”这一步都无法完成。

跨越半个世纪的追寻：真正的涡虫在哪里？

为了找到实验用的涡虫，研究助理扎卡里·凯尔索踏上了一段近乎疯狂的“寻虫之旅”。他先在波士顿查尔斯河上破冰捞虫，又跑到俄勒冈州尤金的小溪中搜寻，再到密歇根湖中捕捞——结果都一样：这些野生涡虫，没有一个能学会任何东西。

更令人沮丧的是，他们找到了当年参与麦康奈尔实验的90多岁老人丹尼尔·金布尔夫妇。两位老人确信，60年前的实验确实成功过。凯尔索甚至专门前往密歇根州，在麦康奈尔当年捕捞涡虫的同一条河流中取样，结果依然令人失望：没有一只涡虫表现出学习能力。

“我们前后试了12种不同的涡虫品系，没有一种能学会。”格什曼无奈地表示。

悬案未解：涡虫“退化”了？还是当年数据有误？

对于为何60年后同样的实验无法复现，科学家们提出了几种解释。

一种看法认为，麦康奈尔及其团队在判断涡虫是否“学习”时可能存在主观偏差，把普通的蠕动误判为“反应”。另一种更离奇的可能性是：涡虫本身在这60年间发生了某种变化——可能是环境污染，也可能是基因漂变所致。但格什曼认为这种可能性极低：“在涡虫数百万年的进化史中，偏偏就在那段时间能学习，然后我们的运气就用光了？这说不通。”

从进化的角度来看，涡虫或许根本不需要记忆。斯奈德指出：“记忆的目的是为了预测和规避危险。但涡虫的再生能力让它们对危险有完全不同的应对方式——被咬成两半都能长回来，还要记忆做什么？”

记忆转移研究：卷土重来？

尽管涡虫实验令人困惑，但“记忆转移”的研究并未止步。2018年，加州大学洛杉矶分校的神经科学家成功将海蛞蝓的记忆通过RNA注射移植到另一只海蛞蝓体内。2021年，普林斯顿大学的研究人员发现，秀丽隐杆线虫可以通过“食用”同类来学习躲避致病细菌。这些研究似乎间接支持了麦康奈尔当年的观点：记忆确实可以通过化学物质转移。

如今，格什曼已经将研究重点从难以捉摸的涡虫转向更可靠的线虫。他表示：“我只希望我们不要再掉进另一个兔子洞了。”不过，一个“虫洞”，看来是不可避免了。

中文翻译：

记忆可否转移——或食用？
引言
那是波士顿的隆冬时节，查尔斯河表面已冻得严严实实。但扎卡里·凯尔索顶着刺骨寒风，终于要终结一个困扰神经科学实验室半个多世纪的谜团。

为此，哈佛大学神经科学家萨姆·格什曼实验室的研究助理凯尔索需要一些蠕虫。具体来说，是涡虫：这种箭形头部的扁形虫，是拥有与人类相似的对称大脑和神经系统的最简单生物之一。通常，实验室会从生物供应公司订购这些广泛使用的模式生物，但邮购的涡虫质量不合格。于是格什曼派凯尔索去查尔斯河冰冷的河岸边捕捉野生涡虫。"我当时想，'我看起来肯定很疯狂，因为我正用锤子敲冰，'"凯尔索回忆道，"所以我穿了更偏商务风格的商务休闲装。"

这并非凯尔索最后一次陷入这种境地。查尔斯河的涡虫最终也不合用。2025年3月他在俄勒冈州尤金市附近溪流中捕获的涡虫同样不行。那年六月他在密歇根湖垂钓的涡虫——这次他穿着齐大腿根的高筒防水靴——也不行，当时野餐的家庭在岸边目瞪口呆地看着他。凯尔索勤勤恳恳地翻开石头，用绑在绳子上的肉块做诱饵，甚至照着古老指南《密歇根淡水三肠涡虫》里的地图寻找。但他的冒险一无所获。当然，他捉到了大量涡虫。可回到格什曼的实验室后，没有一只涡虫能做它们该做的事。

20世纪60年代，一位名叫詹姆斯·麦康奈尔的古怪行为心理学家曾让科学界相信：涡虫能像巴甫洛夫的狗一样被经典条件反射训练——而且这种训练的记忆可以通过同类相食在涡虫之间转移。这些离奇的发现被其他科学家复制，训练涡虫成了高中科学展的保留项目。如今60年过去，涡虫停止了学习，没人知道原因。

我第一次了解到这个科学谜团，是在为本杂志撰写另一篇关于细胞能记住什么的报道时。当我深入挖掘记忆研究的历史文献，不断看到麦康奈尔奇怪的涡虫实验——它们曾吸引一代科学家，随后彻底消失。涡虫记忆本身已被遗忘。我本打算将其当作历史的偶然一笑了之，直到格什曼在一次采访中不经意提到，除了研究单细胞生物Stentor coeruleus外，他的实验室正试图重现20世纪60年代一些古怪的涡虫实验。我听说过这些实验吗？

我了解到，格什曼渴望在麦康奈尔止步之处继续前行。作为越来越多、将目光投向大脑之外寻找记忆起源和基础的认知科学家之一，他对任何看似无需神经突触网络就能记忆的生物都深感着迷。例如，小小的Stentor coeruleus能根据先前经验修改其行为——对于一个不可能拥有神经元的单细胞生物来说，这堪称壮举。如果麦康奈尔的发现可信，涡虫或许会成为记忆研究的下一代重要模式生物。

问题在于，进展并不顺利。事实上，无论格什曼如何努力训练，他的涡虫什么都不学。

蠕虫能学习吗？当麦康奈尔在20世纪50年代初提出这个问题时，记忆与大脑神经元间突触关联有关的观点才刚刚开始流行。麦康奈尔当时是得克萨斯大学心理学研究生，他推断涡虫——拥有真正神经元的最简单生物之一——因此应该能学习。

他早期的涡虫实验并不特别新颖。他只是用涡虫替代了当时标准经典条件反射研究中的老鼠：反复电击涡虫，同时让它们暴露在强光下。经过一段时间训练，涡虫开始将光与电击联系起来，每当灯光闪烁就提前蜷缩身体。瞧：涡虫会学习了！

涡虫还有更奇特的特点可用于实验。如果将涡虫切成两半，两半都会再生成新涡虫——尾部会长出新头，头部会长出新尾。小至原涡虫1/279的碎片都能在几周内再生成完全正常的成年涡虫，其再生能力如此强大，以至于正如一位早期博物学家所言，涡虫实际上"在刀下永生"。对麦康奈尔来说，这种能力引发了一个问题：当你把涡虫切成两半后，两半都记得吗？

真正的涡虫折磨从这里开始。

20世纪60年代，已是密歇根大学年轻教授的麦康奈尔开始斩首他训练过的涡虫。从断头处长回的涡虫行为与原来一样，会联想到光与电击——考虑到它们原始大脑的保留，这个结果他预料到了。让麦康奈尔惊讶的是，从无头尾部再生出的涡虫也记得。这意味着，无论涡虫的记忆以何种形式存在，它们并非大脑的专属领地。"看起来记忆遍布整个动物全身，"麦康奈尔后来反思道。

兴奋之余，麦康奈尔将实验推得更远。他将涡虫切成越来越小的碎片；每次，再生的片段都保留了记忆。他将训练过涡虫的头缝到未训练涡虫的尾部，但头部老是脱落。他将训练过的涡虫打成匀浆，注射给天真的受体——历史学家拉里·斯特恩将此精细过程比作"用标枪刺穿李子"。最后，他想起有些涡虫同类相食，便将训练过的涡虫匀浆喂给它们的同类。在随后的试验中，"同类相食"的涡虫立即获得了光反应，仿佛它们在回忆而非学习该做什么。

如果说麦康奈尔的实验令人毛骨悚然，他的研究思路则反映了那个时代。20世纪50年代DNA双螺旋的发现揭示了蛋白质和核酸中蕴含的信息之多。记忆的物理痕迹（或称"印迹"）可能具有某种化学基础的观点，对许多科学家而言似乎足够合理。麦康奈尔的相食蠕虫真的吃掉了印迹吗？麦康奈尔当然这么认为。他确信它们的记忆编码在RNA结构中——并且可以在涡虫之间转移。

"用计算机工程的术语来说，信息总是被'输入'计算机，"记者亚瑟·库斯勒后来在一篇赞赏麦康奈尔工作的综述中写道，"在这里，隐喻变成了现实。"

这些都是耸人听闻的发现，麦康奈尔充分利用了媒体关注带来的优势。成为科学家之前，他曾在电台有短暂职业生涯，知道如何将微妙的思想重新包装成精辟的短句。在《时代》和《时尚先生》等杂志上，他豪言壮语地谈论着记忆消费的未来——"钢琴课药丸"和"教授汉堡"。他带着训练过的涡虫上了《史蒂夫·艾伦秀》，并违背其干净利落的发型和角框眼镜给人的印象，自称"麦食人族"。

学生们开始写信给麦康奈尔在密歇根大学的实验室，为学校科学展索要训练涡虫的技巧，而麦康奈尔慷慨分享建议。他认为科学应属于人民；他视自己为当代大卫，向机构巨人歌利亚投掷石子。这使他成为当时最著名的公众科学家之一，但却未能赢得更严肃同行的好感。此外，他在《蠕虫跑者文摘》上发表所有研究——这是一份他实验室发行的反文化期刊。

《蠕虫跑者文摘》"有点像《疯狂杂志》遇上严肃科学期刊"，格什曼最近告诉我。鼎盛时期，它在全球约有2500名订阅者。封面上手绘的盾牌图案是一条双头涡虫，以及拉丁文座右铭"ignotum per ignotius"，大致意为"用更未知解释未知"。1959年的创刊号只有14张油印页，讲述涡虫的照顾与喂养，但很快发展壮大。除了发表数十篇记忆转移论文及相关学术文章，麦康奈尔还欢迎幽默，刊登科幻故事、激昂的社论、学生画的涡虫漫画、恶搞文章和诗歌。

虽然《文摘》如今有点邪典经典的味道，但这种混合让许多读者感到困惑。麦康奈尔最终将刊物一分为二，就像切开涡虫一样，将严肃的一半更名为《生物心理学杂志》（与1973年创刊、目前同行评议的《生物心理学》无关）。但麦康奈尔作为异端和恶作剧者的名声已根深蒂固。

20世纪60年代中期开始出问题。尽管麦康奈尔享受了一段名声与资金的时光——包括在密歇根大学加速获得终身教职——但复制其记忆转移的尝试结果不一致。虽然许多实验显然成功，但失败案例更引人注目。1965年，诺贝尔奖得主、生物化学家梅尔文·卡尔文试图复制麦康奈尔的涡虫实验，即便有麦康奈尔前助手的帮助并使用相同设备，仍以失败告终。他高调发表结果，引发了一场关于涡虫正确处理方法等的激烈争论。

到20世纪70年代，涡虫记忆热潮来了又去。科学家转而研究老鼠、猫、金鱼甚至螳螂。成功证明老鼠记忆转移的研究人员——通过将一个动物的大脑RNA注射给另一个——在《自然》和《科学》等著名期刊上发表成果，使得涡虫模型相比之下黯然失色。但当进一步实验变得不确定时，对记忆转移问题的兴趣逐渐消退。正如科学史家哈里·柯林斯和特雷弗·平奇所言："记忆转移从未被完全否定；它只是不再占据科学想象力。"

（图片来自萨姆·格什曼和扎卡里·凯尔索）

麦康奈尔于1971年关闭实验室，此后长期默默无闻，仅有一次中断——1985年，他成为"大学航空炸弹客"的受害者（爆炸后他暂时失去听力）。他于1990年去世。如果年轻一代科学家知道他的同类相食涡虫，那不过是"神经科学家在睡前讲给学生听的警示故事，用来吓唬他们远离注定失败的项目"，格什曼说。

尽管如此，麦康奈尔非传统的作品和反叛态度在神经科学传说中挥之不去，记忆转移的想法仍是私下着迷的话题。如果麦康奈尔真的成功将记忆喂给了涡虫呢？对于正在寻找方法在分子层面研究记忆并将其与可观察行为联系起来的格什曼而言，这个问题像痒处必须挠一挠。他决定一劳永逸地解决此事。

这一切看似简单直接。2025年春天，格什曼和他的博士后麦迪·斯奈德着手复制麦康奈尔学生艾伦·雅各布森的涡虫训练协议。雅各布森的论文是涡虫记忆转移时期最严谨的，格什曼和斯奈德严格照做。"我们需要一个行为基础，以便研究这些极其不稳定的动物中驱动记忆的回路，"斯奈德说，"这些回路是否用于记忆巩固或存储？因为如果你失去头，所有回路都消失了，那么存储记忆的机制是什么？"

然而，尽管全力以赴，他们无法像雅各布森、麦康奈尔以及20世纪60年代许多其他人那样做到：让涡虫形成条件反射，在光照下蜷缩身体（他们于2026年4月在biorxiv.org上报告了结果）。"我真是百思不得其解，"格什曼说。他原以为记忆转移会是实验中最不靠谱的部分——而不是一开始就无法让涡虫形成记忆。

他们与其他研究涡虫的实验室交流。尝试不同刺激。将涡虫影像通过机器学习流程分析。绝望之下，凯尔索和斯奈德甚至参观了哈佛科学博物馆，观察一种老式"感应线圈"——20世纪中期涡虫科学中使用的电击装置。但毫无线索。

凯尔索寻找麦康奈尔可能仍在世的前合作者。运气不错，他找到了丹尼尔·金布尔及其妻子里瓦的联系方式，两人都曾在麦康奈尔实验室工作。现年九旬的他们住在俄勒冈州尤金市。凯尔索打电话时发现，他们不仅负责麦康奈尔20世纪60年代大部分实验，还将《蠕虫跑者文摘》的全部印刷档案保存在地下室的箱子里。

凯尔索和斯奈德买了去尤金的机票。两天时间里，他们边吃着自制的饼干和无数杯茶，边尽最大努力从金布尔夫妇那里吸收信息。手动扫描《文摘》过刊的间隙，他们在附近跳溪越涧，用砂锅盛满带泥沙的淡水。回到金布尔夫妇的厨房桌前，两代科学家看着泥沙沉淀，等着看会有什么蠕虫出现。

（图片来自Taisaku Nogi, Dan Zhang, John D. Chan, Jonathan S. Marchant）

毕竟，麦康奈尔就是这么做的。他不使用实验室品系的涡虫，而是从密歇根大学附近的一个湖泊获取。因此，凯尔索不想放过任何可能，最后一次前往麦康奈尔在密歇根以前的捕捉地。他带着装满涡虫的塑料管回来，但没有一只会学习。"到某个时候，我们有了大约12种不同的涡虫品系，没有一种显示出任何学习能力，"格什曼说。

据斯奈德说，金布尔夫妇绝对相信他们在20世纪60年代的条件反射实验是成功的。涡虫确实学会了——他们确信。那个时代的文献似乎支持他们的确信；至少有36个实验室报告了类似结果。那么，为什么今天用完全相同的实验方法、相同的实验室规程、甚至从同一片密歇根水域捕获的相同涡虫，它们却完全无法被教育呢？

斯奈德说，一种解释是麦康奈尔、金布尔夫妇以及所有其他"蠕虫跑者"在评分涡虫行为时标准不一致，可能将更普通的涡虫"转身"误认为是光反应的明确"蜷缩"。每个科学家都是时代的产物，以无数常常不可见的方式受到社会条件、资金压力以及——在这个案例中——高度魅力型领袖的影响。这种解释让斯奈德高度意识到自己潜在的偏见。"整个项目期间，"她告诉我，"我一直在想，'现在我们在神经科学模型中理所当然接受的东西，以及我们对已知和未知的假设中，有哪些是我真正应该注意的？'"

一个更遥远但并非不可能的可能性是：涡虫本身在过去六十年里发生了某种变化——成为污染或遗传漂变的受害者。格什曼认为这种情况不太可能。"一群研究者恰好在这种现象发生的特定时间做了这些研究，这种可能性有多大？"他难以置信地问，"他们在涡虫数百万年的进化中碰上了极好的运气？然后我们的运气用完了？"

无论原因如何，到2026年，尽管有神经系统和简单大脑，涡虫不学习。从进化角度看，这或许说得通。"我们学会某种程度的联想，某种程度上是为了能预测危险并避免它，"斯奈德说。但涡虫与危险的关系不同。它们的再生生理特性——对麦康奈尔的实验如此关键——保护它们免受钝伤。被咬成两半，它们只需重新长回去。记忆对这样的生物有什么用？"那完全是另一个哲学难题，"她说。

现在是解决这类难题的大好时机。涡虫学习或许是一条死胡同，但用其他生物进行的记忆转移实验正重新成为科学流行趋势——而且这些实验似乎奏效。2018年，加州大学洛杉矶分校的神经科学家大卫·格兰兹曼对海兔Aplysia californica进行了记忆移植——这种海兔因其相对简单的神经系统和巨大的神经元成为记忆研究的宠儿模式生物。训练这些海兔对尾部电击做出反应后，格兰兹曼通过直接注射遗传物质，将敏感化从一只海兔转移到另一只。这表明记忆的某些方面存储在RNA中，这正是麦康奈尔的主张。

然后，在2021年，普林斯顿大学遗传学家科琳·墨菲发现，线虫Caenorhabditis elegans——一种只有302个神经元的微小线虫——可以通过吃掉、甚至只是在曾惨痛学习过的线虫匀浆中游动，来学会避开致病细菌。墨菲的团队发现了一个名为Cer1的逆转录转座子——一段跳跃的遗传物质——它似乎在个体之间"携带记忆"，她说。几年后，印度科学研究所的一个小组发表论文，提出训练过的C. elegans线虫会释放胞外囊泡——含有遗传信息的小脂质颗粒——能将训练成果传递给天真同类。

这些研究者中没有一个人像麦康奈尔那样张扬，但他们的工作表明，他对蠕虫记忆的看法或许终究是对的。他只不过押错了蠕虫种类——并在证据不一致的情况下加倍下注。最终，他失去了名声，但他纯粹的热情激起了另一位非传统科学家的好奇心。幸运的是，这位科学家正遵循证据前行。

在哈佛，格什曼正将焦点从难以捉摸的涡虫转向更易理解的C. elegans线虫。虽然切成两半后不会再生，但C. elegans是神经科学中长期使用的模式生物——而且已被一致证明能学习。随着新实验的展开，格什曼持谨慎乐观态度。"我只是希望我们不会陷入另一个兔子洞，"他告诉我。而蠕虫洞——那是肯定的。

英文来源：

Are Memories Transferable — or Edible?
Introduction
I
t was the dead of winter in Boston. The surface of the Charles River was frozen solid. But Zachary Kelso braved the biting cold to finally put to rest a mystery that has haunted neuroscience labs for over half a century.
To do that, Kelso, a research assistant in the Harvard lab of the neuroscientist Sam Gershman, needed some worms. Specifically, planarians: arrow-headed flatworms, which are among the simplest creatures to possess a brain and a nervous system with bilateral symmetry like ours. Normally, labs order these widely used model organisms from biological supply companies. But the mail-order worms weren’t up to snuff. So Gershman had dispatched Kelso to the Charles’ icy banks to catch some wild ones. “I thought, ‘I’m going to look crazy because I’m using a hammer to beat through the ice,’” Kelso recalled. “So I wore the more business end of business casual.”
It wouldn’t be the last time Kelso found himself in this situation. The Charles River planarians, it turned out, didn’t cut it either. Neither did the worms he sourced while stream-hopping around Eugene, Oregon, in March 2025. Nor did the ones he fished from Michigan lakes that June — this time in thigh-high waders — while picnicking families gawked from shore. Kelso diligently turned over rocks, angled with bits of meat tied to a string, and even followed maps from a vintage guidebook called The Fresh-Water Triclads of Michigan. But his adventure was fruitless. Sure, he caught plenty of planarians. But back in Gershman’s lab, none of them would do what they were supposed to do.
In the 1960s, an eccentric behavioral psychologist named James McConnell convinced the scientific establishment that planarian worms, like Pavlov’s dogs, could be classically conditioned — and that memories of this training could be transferred from worm to worm through cannibalism. These bizarre findings were replicated by other scientists, and worm training became a staple of high school science fairs. Now, 60 years later, the worms have stopped learning, and nobody knows why.
I first learned about this scientific mystery while reporting another piece for this magazine about what a cell can remember. As I dug into the historical literature on memory research, I kept coming across McConnell’s strange worm experiments, which captivated a generation of scientists before disappearing entirely. Planarian memory had itself been forgotten. I was content to dismiss it as a fluke of history until Gershman mentioned, in passing during an interview, that in addition to their work with the unicellular ciliate Stentor coeruleus, his lab was attempting to reproduce some wacky worm experiments from the 1960s. Had I heard of them?
Gershman, I learned, was keen to pick up where McConnell had left off. As part of a growing cohort of cognitive scientists looking beyond the brain for clues to the origins and basis of memory, he’s fascinated by any creature that seems to remember without the benefit of neural, synaptic networks. Little Stentor coeruleus, for example, can modify its behavior based on previous experience — quite a feat for a single-celled creature that can’t possibly have a neuron. Planarian worms, if McConnell’s findings were to be believed, might be the next great model organism for memory research.
The trouble was, it wasn’t going well. In fact, no matter how hard Gershman tried to train them, none of his planarians would learn a thing.
Can a worm learn? When McConnell posed the question in the early 1950s, the notion that memory had something to do with synaptic associations between neurons in the brain was just beginning to gain currency. McConnell, then a graduate student in psychology at the University of Texas, reasoned that planarians — among the simplest creatures with true neurons — should therefore be able to learn.
His early worm experiments were not particularly novel. He simply substituted worms for rats in what were, at the time, standard classical conditioning studies: repeatedly shocking the worms while exposing them to a bright light. After a period of this training, the worms came to associate the light with the shock and scrunched their bodies in anticipation whenever the light flashed. Voilà: worm learning!
Planarians have stranger features to offer for experiments. If a planarian is chopped in half, both halves will regrow into a new worm — the tail will grow a new head, and the head will grow a new tail. A fragment as small as 1/279 of the original worm can regrow into a completely normal adult worm in a matter of weeks, a regenerative capacity so powerful that, as one early naturalist put it, planarians are effectively “immortal under the edge of the knife.” For McConnell, this ability begged the question: When you chop a worm in half, do both halves remember?
This is where the real worm torture began.
In the ’60s, McConnell, by then a young professor at the University of Michigan, started beheading his trained planarians. The worms that grew back from the severed heads behaved as the originals had, associating the light with the shock — a result he expected, given the preservation of their primitive brains. What surprised McConnell was that the worms that regenerated from headless tails remembered, too. This meant that whatever form the worms’ memories took, they weren’t the exclusive purview of the brain. “It appeared that the memories were laid down throughout the animal’s body,” McConnell later reflected.
Thrilled, McConnell pushed his experiments further. He cut the worms into smaller and smaller pieces; each time, the regenerated segments retained the memory. He stitched the heads of trained worms onto untrained tails, but they kept falling off. He pureed trained worms and injected them into naïve recipients, a delicate process that the historian Larry Stern has compared to “impal[ing] a prune with a javelin.” Finally, remembering that some planarians are cannibals, he fed trained-worm puree to their brethren. In subsequent trials, the “cannibal” worms picked up the light response right away, as though they were remembering, rather than learning, what to do.
If McConnell’s experiments appear gruesome, his line of inquiry was of his time. The discovery of the DNA helix in the 1950s had revealed just how much information is packed into proteins and nucleic acids. The notion that the physical traces of memories, or “engrams,” might have some chemical basis seemed plausible enough to many scientists. Could McConnell’s cannibal worms have eaten an engram? McConnell certainly thought so. He was convinced that their memories were encoded in the structure of their RNA — and could be transferred from worm to worm.
“In the jargon of computer engineering, information is always ‘fed’ into a computer,” the journalist Arthur Koestler later wrote in an appreciative survey of McConnell’s work. “Here the metaphor became flesh.”
These were sensational findings, and McConnell took every advantage of the media attention they generated. Before becoming a scientist, he had had a brief career in radio, and he knew how to repackage nuanced ideas as pithy soundbites. In magazines such as Time and Esquire, he spoke grandly of a future of memory consumption — of “piano lesson pills” and “professor burgers.” He brought his trained worms onto The Steve Allen Show, and, belying his clean-cut hair and horn-rimmed glasses, dubbed himself “McCannibal.”
Students began writing to McConnell’s lab at the University of Michigan to ask for worm-training tips for their school science fairs, and McConnell shared advice. Science, he believed, should be for the people; he saw himself as a latter-day David pitching stones at institutional Goliaths. This made him one of the most famous public scientists of his era, but it did not endear him to more serious peers. It also didn’t help that he published all his research in The Worm Runner’s Digest, a countercultural journal he distributed from his lab.
The Worm Runner’s Digest was “sort of Mad Magazine meets a serious scientific journal,” Gershman told me recently. At its peak, it had some 2,500 subscribers around the world. The hand-drawn shield on its cover featured a two-headed planarian and the Latin motto ignotum per ignotius, which roughly translates to “the unknown explained through the even more unknown.” Its 1959 inaugural issue consisted of only 14 mimeographed pages about the care and feeding of planarians, but it quickly grew. In addition to publishing dozens of memory transfer papers and related scholarship, McConnell welcomed humor and printed science fiction stories, rousing editorials, student-drawn planarian cartoons, spoof articles, and poems.
While the Digest is now something of a cult classic, the mix proved confusing for many readers. McConnell eventually cut the publication in half, not unlike a planarian worm, and renamed the serious half The Journal of Biological Psychology (no relation to the current peer-reviewed journal Biological Psychology, founded in 1973). But McConnell’s reputation as a heretic and prankster was well established.
The wheels started to come off in the mid-1960s. Although McConnell enjoyed a period of fame and funding — including an accelerated path to tenure at the University of Michigan — attempts to replicate his memory transfers yielded inconsistent results. While many apparently succeeded, the failures were more visible. In 1965, the Nobel Prize–winning biochemist Melvin Calvin tried to replicate McConnell’s worm experiments and failed, even with the help of some of McConnell’s former assistants and using the same device. His high-profile publication of the results sparked an acrimonious debate about, among other things, proper worm handling.
By the 1970s, the planarian memory fad had come and gone. Scientists had moved on to rats, cats, goldfish, and even praying mantises. Researchers showing successful memory transfers in rats — by injecting brain RNA from one animal to another — had published their findings in prestigious journals such as Nature and Science, making the planarian model seem unimpressive in comparison. But when further experiments proved inconclusive, interest in the question of memory transfer petered out. As the science historians Harry Collins and Trevor Pinch put it, “memory transfer was never quite disproved; it just ceased to occupy the scientific imagination.”
Courtesy of Sam Gershman and Zachary Kelso
McConnell closed his laboratory in 1971, and his long period of subsequent obscurity was broken only once, in 1985, when he became a victim of the Unabomber. (He lost his hearing temporarily after the blast.) He died in 1990. If a younger generation of scientists is familiar with his cannibal planarians, it’s as “a cautionary tale that neuroscientists tell to their students at bedtime to scare them away from ill-fated projects,” Gershman said.
Still, McConnell’s unconventional work and contrarian attitude has lingered in neuroscience lore, and the idea of memory transfer remains a subject of private fascination. What if McConnell really did manage to feed a memory to a worm? For Gershman, who is searching for a way to study memory at a molecular level and connect it to observable behavior, the question was an itch that had to be scratched. He decided to settle the matter once and for all.
It all seemed straightforward enough. In the spring of 2025, Gershman and Maddie Snyder, one of his postdocs, set out to reproduce the worm-training protocol of one of McConnell’s students, Alan Jacobson. Jacobson’s papers were the most rigorous of the planarian memory transfer era, and Gershman and Snyder followed them to the letter. “We wanted a behavioral basis to be able to study the circuits that are driving memory in these extremely unstable animals,” Snyder said. “Are those circuits at all being used for memory consolidation or storage? Because if you lose your head and all those circuits are gone, then what is the mechanism of storing memory?”
Despite their best efforts, however, they couldn’t do what Jacobson, McConnell, and so many others had done back in the 1960s: condition the worms to scrunch their bodies in response to light. (They reported the results on biorxiv.org in April 2026.) “I was really scratching my head about this,” Gershman said. He’d assumed that the memory transfer would be the dodgy part of the experiment — not getting the worms to form a memory in the first place.
They talked to other planarian labs. They tried different stimuli. They ran the planarian footage through a machine learning pipeline. In desperation, Kelso and Snyder even visited the Harvard Science Museum to examine a vintage “inductorium,” an electric-shock contraption used in midcentury worm science. But it offered no clues.
Kelso searched for any of McConnell’s former collaborators who might still be alive, and through a stroke of luck he found contact information for Daniel Kimble and his wife, Reeva, who had both worked in McConnell’s lab. Now in their 90s, they live in Eugene, Oregon. When Kelso called them, he discovered that not only did they run most of McConnell’s experiments in the 1960s, but they’d also kept the entire print archive of The Worm Runner’s Digest in a box in their basement.
Kelso and Snyder bought tickets to Eugene. Over the course of two days, while consuming plates of homemade cookies and countless cups of tea, they absorbed everything they could from the Kimbles. On breaks from hand-scanning back issues of the Digest, they went stream-hopping nearby and filled casserole dishes with silty fresh water. Back at the Kimbles’ kitchen table, the two generations of scientists watched the silt settle to see what worms might emerge.
Taisaku Nogi, Dan Zhang, John D. Chan, Jonathan S. Marchant
This, after all, is what McConnell did. Rather than using laboratory strains of planarians, he sourced his from a lake near the University of Michigan. And so, not wanting to leave any stone unturned, Kelso made one final trip to McConnell’s former fishing grounds in Michigan. He returned with plastic tubes full of worms, but not a single one was a learner. “At some point, we had like 12 different strains of planaria, none of which showed any learning,” Gershman said.
As Snyder tells it, the Kimbles were absolutely convinced that their conditioning experiments in the 1960s had worked. The worms learned — they were sure of it. The literature of the era seems to support their certainty; at least 36 labs reported similar results. So why is it that when the exact same experiments are done today, using the same laboratory protocol and even the same worms, fished from the same Michigan waters, planarian worms are utterly uneducable?
One explanation, Snyder said, is that McConnell, the Kimbles, and all the other “worm runners” were inconsistent in how they scored the planarians’ behavior and may have misinterpreted more anodyne worm “turns” for the definitive “scrunch” of the light reaction. Every scientist is a product of their time, after all, influenced in myriad, often invisible ways by sociological conditions, funding pressures, and, in this case, a highly charismatic leader. This interpretation made Snyder hyperaware of her own potential biases. “Throughout this entire project,” she told me, “I was like, ‘What are the things that I am taking for granted now in our models of neuroscience, and our assumptions of what is known and unknown, that I should really notice?’”
A more remote possibility is that planarian worms themselves have somehow changed over the last six decades — falling victim to pollution or genetic drift. Gershman finds this scenario unlikely. “What are the chances that a bunch of researchers just happened to do these studies at the particular time when this phenomenon happened?” he asked, incredulous. “They just got extremely lucky, in the millions of years of planarian evolution? And then our luck ran out?”
No matter the reason, in 2026, despite their nervous system and simple brains, planarians don’t learn. From an evolutionary perspective, this might actually make sense. “The reason that we learn associations, to some degree, is so that we can predict danger and avoid it,” Snyder said. But planarians have a different relationship to danger. Their regenerative physiology, so key to McConnell’s experiments, protects them from blunt trauma. Bitten in half, they simply grow back. What use is memory to such a creature? “That’s a whole other philosophical conundrum,” she said.
It’s a great time to be wrestling with such conundrums. Planarian learning may be a dead end, but memory transfer experiments with other organisms are back in scientific vogue — and those experiments appear to be working. In 2018, the neuroscientist David Glanzman of the University of California, Los Angeles performed a memory transplant on the sea slug Aplysia californica, a darling model organism for memory research owing to its relatively simple nervous system and gigantic neurons. After training the slugs to respond to a shock to their tails, Glanzman was able to transfer the sensitization from one slug to another via a direct injection of genetic material. This suggested that some aspect of the memory was stored in RNA, which was McConnell’s contention.
Then, in 2021, the Princeton University geneticist Coleen Murphy found that Caenorhabditis elegans worms — microscopic roundworms with 302 neurons to their name — could learn to avoid a pathogenic bacterium by eating, or even just swimming around in, pureed worms who had learned the hard way. Murphy’s group identified a retrotransposon, a jumping segment of genetic material, called Cer1, that appears to “carry a memory” between individuals, she said. A few years later, a group at the Indian Institute of Science published a paper suggesting that trained C. elegans worms release extracellular vesicles — small lipid particles containing genetic information — that can impart their training to their naïve counterparts.
None of these researchers are half as flashy as McConnell was, but their work indicates that he may have been right about worm memory after all. He just bet on the wrong kind of worm — and doubled down on it, despite inconsistent evidence. In the end, he lost his reputation, but his sheer gusto sparked the curiosity of another unconventional scientist. Fortunately, this one’s following the evidence.
At Harvard, Gershman is shifting his focus from the inscrutable planarian to the more legible C. elegans. It may not regenerate when it’s cut in half, but C. elegans is a long-standing model organism in neuroscience — and it’s been consistently shown to learn. With new experiments underway, Gershman is cautiously optimistic. “I just hope we’re not going down another rabbit hole,” he told me. A wormhole, on the other hand — that’s for certain.